Papermachine fabric

ABSTRACT

A papermachine fabric for dewatering a fibrous web in a machine producing a fibrous web. The fabric including a laid scrim having at least one layer of longitudinal threads and at least one layer of transverse threads crossing the layer of longitudinal threads. At least a selection of the longitudinal threads being laid at different distances both symmetrically and asymmetrically in relation to one another, the distance between two adjacent threads changing in the course of a laying pattern.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a papermachine fabric for dewatering a fibrousweb in a machine producing a fibrous web, having a laid scrim.

2. Description of the Related Art

A papermachine fabric is known, for example, from European patentapplication EP 1 357 223 A1, having longitudinal threads runningparallel to one another and transverse threads running parallel to oneanother. The threads are adhesively bonded to one another at crossingpoints using an adhesive. The adhesive can be, for example, a hot-meltadhesive, a diffusion adhesive, a contact adhesive and/or a reactiveadhesive. The use of the adhesive opens up the possibility of effectinga direct connection between the longitudinal and transverse threads atthe crossing points.

Apart from the not inconsiderable production costs of the papermachinefabric because of the use of an adhesive together with its propertiesand peculiarities, the load distribution of the papermachine fabric,which is predefined by the production and not optimal for everyapplication on account of the mutually parallel alignment of thethreads, is disadvantageous.

SUMMARY OF THE INVENTION

The present invention is based on the object of developing apapermachine fabric of the type mentioned at the beginning in such a waythat, in addition to an optimal load distribution, a beneficial poresize for each application is also ensured.

According to the present invention, this object is achieved in that atleast a selection of threads of a layer are laid at different distancesboth symmetrically and asymmetrically in relation to one another, thedistance between two adjacent threads is preferably changed in thecourse of their laying pattern. The change in the respective distance iscarried out continuously, abruptly, periodically, in some regions andthe like. In addition, the preferable change in the distance between twoadjacent threads in the course of their laying pattern preferablyassumes a value ≧1%, preferably ≧3%, in particular ≧5%, based on thelength of a respective thread.

This individual laying of at least a selection of threads of a layerprovides for the first time a papermachine fabric having a laid scrimwhich, in addition to the advantage of an optimal load distribution,also provides the advantage of determinable and beneficial pore sizes asa result of the resulting “meshes” in the vertical arrangement ofdifferent layers.

The term “thread” is used here as broadly as possible. The thread can,for example, have been produced by way of an additive and also reductivefabrication method. Furthermore, its material can include a PolyethyleneTerephthalate (PET), Polyamide (PA) in all modifications, Polypeptide(PP), Polyphenylene Sulfide (PPS), Polyetherketone (PEK),Polyetherketoneketone (PEKK), elastic Polyethylene (PE), PolybutyleneTerephtalate (PBT), Poly Trimethylene or Poly Terephthalate (PTT) orcombinations thereof. It can also be reinforced, for examplefiber-reinforced with glass fibers, carbon fibers and/or ceramic fibers.In addition, it can also be a multi-component thread, such as asheath-core thread, a side-by-side thread and the like. Its properties,in particular tensile strength, stretch and the like, are in general notsubject to any restrictions.

In an advantageous refinement of the present invention, a selection ofthreads of the two layers are laid at different distances bothsymmetrically and asymmetrically in relation to one another. Thispermits, amongst other things, improved load distributions withindividual pore sizes of the laid scrim.

For example, the threads of a layer can be laid symmetrically orasymmetrically in relation to one another in a plurality of groups, andthe groups of threads of a layer can in turn be laid symmetrically orasymmetrically in relation to one another.

In order that the marking, of the fibrous material to be dewatered bythe fabric, is kept as diffuse as possible, in particular also over aplurality of layers, the different distances are selected in accordancewith a pattern, randomly or in combination.

In another embodiment of the present invention, at least two adjacentlayers of threads with the same or approximately the same alignment, atleast in some regions, which have a complementary position of threads inrelation to one another is provided. In this case, interspaces can beprovided between the threads of a layer, at least in some regions, whichare filled with a permeable material. The permeable material ispreferably at least one polyurethane foam. Such an arrangement has thesubstantial advantage that the complementary layers are able todistribute optimally the pressure pulses acting in a press of a paper orboard machine and, at the same time, always have adequate permeability.The filling polyurethane foam is generally applied only when the scrimis arranged on a two-dimensional carrier medium, such as a nonwovencarrier medium. This is necessary since the foam would otherwise flowthrough the holes present in the scrim and thus not result in ahomogeneous surface. The pores depend, inter alia, on the viscosity ofthe polyurethane foam and the existing pore size.

In order to be able to influence this permeability further, a layer thatis preferably permeable over its entire area is introduced, at leastbetween the two adjacent layers of threads, at least in some regions.Furthermore, the threads arranged above one another of two adjacentlayers can have at least one different property, at least in someregions. They can therefore complement one another in their function.The threads of one layer have the at least one different propertyalternately and offset with respect to the threads of the adjacentlayer. Therefore, overall, a constant feature is obtained with, at thesame time, optimized permeability and/or pressure behavior.

The different property is preferably at least the thread thickness, thethread hardness, the thread structure, the thread material or the like.Of course, further characteristics of the thread can also form thedifferent property. The thread can also be a nonwoven strip or amaterial ribbon, it being conceivable for these to perform otherfunctions as well, such as the production of internal volume or reboundcapacity, in addition to the load-absorbing function.

Furthermore, the common factor in all the configurations described isthat two adjacent layers of threads can run at an angle α, at least insome regions. The angle α can assume a value in the range from 0°≦α≦90°.The threads can therefore, run in a longitudinal, transverse and/ordiagonally oriented alignment in relation to one another. Of course, thethreads of an individual layer can also run at the aforementioned angleα in relation to one another.

In addition, the papermachine fabric can have at least two, preferably aplurality of, layers of laid scrims according to the invention, itpreferably being possible for at least two, preferably all, of thelayers of laid scrims to be separated from one another by a separatinglayer in each case. However, in the final stage of the production of thefabric, the separating layers must enter into an intimate connectionwith the laid scrims.

In one embodiment of the present invention, the papermachine fabric is apress felt for dewatering a fibrous web in a machine producing a fibrousweb, having a laid scrim including at least one layer of longitudinalthreads and at least one layer of transverse threads crossing thelongitudinal threads. The fabric has at least one fine fiber batt on theside of the fibrous web, at least one coarse fiber batt on the carrierside and a central layer having a described laid scrim between the twofiber batts. In this case, the fine fiber batt preferably has a fiberweight ≦5 dtex, whereas the coarse fiber batt preferably has a fiberweight ≧50 dtex. The fiber batt can also consist of a mixture ofdifferent fibers, in this case the fibers having the greatest proportionby weight preferably defining the criterion “fine” versus “coarse”.

The threads of the central layer can be filled with a permeablematerial, in particular polyurethane foam, in their two lateral regions.As already mentioned, the filling polyurethane foam is normally appliedonly when the scrim is arranged on a two-dimensional carrier medium,such as a nonwoven carrier medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows a schematic cross-sectional illustration of an embodimentof a papermachine fabric according to the present invention;

FIGS. 2 and 3 show two partial schematic cross-sectional illustrationsof further embodiments of the papermachine fabric according to thepresent invention; and

FIG. 4 shows a view of exemplary courses of adjacent threads of a layerof the fabrics in FIGS. 1-3.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplifications are not to be construed as limiting the scope ofthe invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1 there isshown a schematic sectional illustration of an embodiment of apapermachine fabric according to the present invention. Papermachinefabric 1 is used for dewatering a fibrous web, not illustrated, in amachine producing a fibrous web. Fabric 1 includes a laid scrim 2, alayer A of longitudinal threads 3.1 to 3.6 and a layer B of transversethreads 4 crossing longitudinal threads 3.1 to 3.6, only one transversethread 4 being visible.

At least a selection of threads 3.1 to 3.6 of layer A at differentdistances A₁ to A₅ are laid both symmetrically and asymmetrically withrespect to one another, the distance B₁ to B₃ between two adjacentthreads 3.1, 3.2; 3.3, 3.4; 3.5, 3.6 preferably changing in the courseof their laying pattern. The change in the respective distance B₁ to B₃can be made continuously, abruptly and/or periodically, in some regions.

Threads 3.1 to 3.6 of layer A are laid symmetrically or asymmetricallyin relation to one another in a plurality of groups G₁ to G₃. Groups G₁to G₃ of threads 3.1 to 3.6 of layer A in turn are laid symmetrically orasymmetrically in relation to one another. In the embodiment of thepresent invention, illustrated in FIG. 1, the different distances A₁ toA₅ are selected in accordance with a pattern, but can also be selectedrandomly or in combination. Longitudinal threads 3.1 to 3.6 of layer Aand transverse threads 4 of layer B run at an angle α, at least in someregions, angle α assuming a value in the range from 0°≦α≦90°.

Now, additionally referring to FIG. 2 there is shown a partial andschematic sectional illustration of another embodiment of papermachinefabric 1 according to the present invention. Two adjacent layers C and Dof threads 5.1 to 5.6 and 6.1 to 6.6 form a laid scrim 2 having the sameor approximately the same alignment, at least in some regions. Layers Cand D have at least one different property, at least in some regions,such as a complementary pairwise positioning of threads 5.1, 6.1, 5.2,6.2, 5.3, 6.3, 5.4, 6.4, 5.5, 6.5, 5.6 and 6.6 in relation to oneanother. Although for purposes of clarity the different property in theembodiment illustrated is the thread thickness, the different propertycan also be the thread hardness, the thread structure, the threadmaterial or the like.

Between threads 5.1 to 5.6 and 6.1 to 6.6 of a layer C or D, interspaces7.1 to 7.5 and 8.1 to 8.5 are provided, at least in some regions, whichare filled with a permeable material 9. The permeable material 9 mayinclude at least one polyurethane foam 10.

Between two adjacent layers C and D of threads 5.1 to 5.6 and 6.1 to6.6, at least in some regions, a layer 11 that is preferably permeableover its entire area is introduced. The two adjacent layers C and D ofthreads 5.1 to 5.6 and 6.1 to 6.6 run at an angle α, at least in someregions. Angle α assumes a value in the range from 0°≦α≦90°. In thepresent case, as already mentioned, angle α assumes a value in theregion of 0°, that is to say the same or approximately the samealignment.

Now, additionally referring to FIG. 3 there is shown a partial andschematic cross-sectional illustration of yet another embodiment ofpapermachine fabric 1 according to the present invention. Here again,two adjacent layers E and F of threads 12.1 to 12.5 and 13.1 to 13.5form a laid scrim 2 and have the same or approximately the samealignment, at least in some regions. Layers E and F having at least onedifferent property, at least in some regions, which have a complementarypairwise positioning of threads 12.1, 13.1, 12.2, 13.2, 12.3, 13.3,12.4, 13.4, 12.5 and 13.5 in relation to one another. In this case,threads 12.1 to 12.5 of layer E have the at least one different propertyalternately and offset with respect to threads 13.1 to 13.5 of adjacentlayer F. The different property in the embodiment illustrated is thethread thickness. In a further embodiment, (not illustrated) it can alsobe the thread hardness, the thread structure, the thread material or thelike.

For example, thread 12.1 of layer E has a small thread thickness,adjacent thread 13.1 of layer F, by contrast, has a large threadthickness. Adjacent thread 12.2 and 13.2 of respective layers E and F inturn has a contrary thread thickness. These geometries are repeated, sothat ultimately a uniform thickness of laid scrim 2 is provided. Thesame thread thicknesses can of course also extend over a plurality ofthreads of the same layer and/or with a pattern in the same layer.

The two adjacent layers E and F of threads 12.1 to 12.5 and 13.1 to 13.5run at an angle α, at least in some regions. Angle α having a value inthe range from 0°≦α≦90°. In the present case, as already mentioned,angle α assumes a value in the region of 0°, that is to say the same orapproximately the same alignment.

Laid scrim 2, illustrated in FIGS. 1-3 can, for example, be part of acentral layer 15 of a press felt 14, which has a fine fiber batt 16 onthe fibrous web side and a coarse fiber batt 17 on the carrier side.This structure of press felt 14 is illustrated in FIG. 2. Central layer15 is arranged between two fiber batts 16 and 17, which can have stillfurther layers of threads. In addition, illustrated threads 5.1 to 5.6and 6.1 to 6.6 of central layer 15 can be filled with a permeablematerial 18, in particular polyurethane foam, in lateral regions H andI. Layer 11, which is preferably permeable over its entire area, doesnot necessarily have to be present in this embodiment.

Now, additionally referring to FIG. 4 there is shown a view of exemplarycourses of adjacent threads 3.1 to 3.11 of a layer. In this case,threads 3.1 to 3.11 can be ordered in the longitudinal direction and inthe transverse direction and also in combination. It can be seen thatthe respective distance B₁ to B₆ between two adjacent threads 3.1 to3.11 changes in the course of their laying pattern. The change in therespective distance B₁ to B₆ can take place continuously (threads 3.1,3.2), abruptly (threads 3.3, 3.4), periodically, in some regions(threads 3.5, 3.6), varying continually (threads 3.7, 3.8; 3.10, 3.11),pseudo-parallel (threads 3.9, 3.10) and the like. The coursesillustrated are, as already mentioned, purely exemplary. Of course, itis possible for there to be both further courses, not illustrated, andalso combinations of courses.

In summary, it is to be recorded that, by means of the invention, apapermachine fabric of the type mentioned at the beginning is developedin such a way that, in addition to an optimal load distribution, abeneficial pore size for every application is also ensured.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

LIST OF DESIGNATIONS

1 Papermachine fabric

2 Laid scrim

3.1 to 3.6 Longitudinal thread

4 Transverse thread

5.1 to 5.6 Thread

6.1 to 6.6 Thread

7.1 to 7.5 Interspace

8.1 to 8.5 Interspace

9 Material

10 Polyurethane foam

11 Layer

12.1 to 12.5 Thread

13.1 to 13.5 Thread

14 Press felt

15 Central layer

16 Fiber batt

17 Fiber batt

18 Material

A Layer

A₁ to A₅ Distance

B Layer

B₁ to B₃ Layer

C Layer

D Layer

E Layer

F Layer

G₁ to G₃ Group

H Lateral region

I Lateral region

α Angle

1. A papermachine fabric for dewatering a fibrous web in a machineproducing a fibrous web, the fabric comprising: a laid scrim including:at least one layer of longitudinal threads; and at least one layer oftransverse threads crossing said layer of longitudinal threads, at leasta selection of said longitudinal threads being laid at differentdistances both symmetrically and asymmetrically in relation to oneanother, the distance between two adjacent threads changing in thecourse of a laying pattern.
 2. The papermachine fabric of claim 1,wherein a selection of threads of said layer of longitudinal threads andsaid layer of transverse threads are laid at different distances bothsymmetrically and asymmetrically in relation to one another.
 3. Thepapermachine fabric of claim 1, wherein said longitudinal threads arelaid symmetrically or asymmetrically in relation to one another in aplurality of groups.
 4. The papermachine fabric of claim 3, wherein saidgroups of said longitudinal threads are laid symmetrically orasymmetrically in relation to one another.
 5. The papermachine fabric ofclaim 4, wherein said different distances are selected in accordancewith at least one of a pattern, randomly and a combination thereof. 6.The papermachine fabric of claim 1, wherein at least two adjacent layersof said at least one layer of longitudinal threads and said at least onelayer of transverse threads having approximately the same alignment, inat least some regions have a complementary positioning of threads inrelation to one another.
 7. The papermachine fabric of claim 6, whereininterspaces are provided between threads of said at least two adjacentlayers in at least some regions, said interspaces being filled with apermeable material.
 8. The papermachine fabric of claim 7, wherein saidpermeable material includes at least one polyurethane foam.
 9. Thepapermachine fabric of claim 6, wherein a layer that is permeable isintroduced between said at least two adjacent layers of threads at leastin some regions.
 10. The papermachine fabric of claim 9, wherein threadsarranged above one another of said two adjacent layers have at least onedifferent property in at least some regions.
 11. The papermachine fabricof claim 10, wherein threads of one of said two adjacent layers have theat least one different property alternately and offset with respect tothe threads of another of said two adjacent layers.
 12. The papermachinefabric of claim 10, wherein said different property is at least one ofthread thickness, thread hardness, thread structure and thread material.13. The papermachine fabric of claim 10, wherein said at least twoadjacent layers of threads run at an angle α in at least some regions,said angle α assuming a value in the range of 0°≦α≦90°.
 14. Thepapermachine fabric of claim 1, further comprising a plurality of layersof laid scrims.
 15. The papermachine fabric of claim 14, wherein atleast two of said plurality of layers of laid scrims are separated fromone another by a separating layer.
 16. A press felt for dewatering afibrous web in a machine producing a fibrous web, the fabric comprising:at least one fine fiber batt on the side of the fabric facing thefibrous web; at least one coarse fiber batt on the side of the fabricfacing away from the fibrous web; and a central layer having a laidscrim between said fine fiber batt and said coarse fiber batt, said laidscrim including: at least one layer of longitudinal threads; and atleast one layer of transverse threads crossing said layer oflongitudinal threads.
 17. The fabric of claim 16, wherein saidlongitudinal threads and said transverse threads of said central layerare filled with a permeable material.
 18. The fabric of claim 17,wherein said permeable material is polyurethane foam in two lateralregions of the fabric.